JP2000291770A - Ball screw - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the increase in a dynamic torque by restraining the wear of a ball in a low speed area without dropping a load capacity, in an use in which the ball screw with a high load capacity is requested, such as an electric injection molding machine and electric press machine. SOLUTION: This ball screw stores lots of balls 32 in the ball screw grooves 31, 31' inside a nut 8. The balls 32 are formed by a load ball and a spacer ball with a smaller diameter than the load ball and respective balls are arranged so that one spacer ball is interposed between two load balls and this is used restrictedly to the use in which the swing stroke H of the screw shaft 7 or nut 8 is the relationship of H<=3×L with respect to the lead L of the ball screw grooves 31, 31'.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ball screw used for a rocking portion frequently used under a high load load such as an electric injection molding machine and an electric press machine.

[0002]

2. Description of the Related Art Injection molding machines and press machines are increasingly using ball screws instead of conventional hydraulic drive systems. In these cases, the hydraulic cylinder that applies a high load is replaced with a ball screw, so that the ball screw is required to have a load capacity that can withstand a high load. To increase the load capacity of the ball screw, increase the shaft diameter or ball diameter, decrease the curvature of the ball groove on which the ball rolls, or increase the number of circulations by using multiple threads to increase the ball number in the nut. Means such as increasing the number are conceivable.

[0003] In a ball screw used in a machine tool, the stroke H of the nut is a sufficiently large value relative to the lead L of the ball screw groove, that is, H> 3 × L. The load capacity could be increased by taking measures. However, under the condition that the nut stroke H is smaller than the lead L, that is, H ≦ 3 × L,
In applications that are used under repeated high load loads,
The frictional force between adjacent balls increases with the swinging motion of the balls in the nut, which causes a problem that increases the dynamic torque and causes the balls to wear out early.

When a ball screw nut of a normal constant-pressure preload is used for swinging, as shown in FIG. 4A, the rolling surface 41 of the ball screw groove on the screw shaft side and the rolling of the ball screw groove on the nut side are used. In the case of a so-called total load type in which all the balls 43 interposed between the running surfaces 42 have the same diameter and all the balls 43 support a load, all the balls 43 rotate in the same direction. Friction increasing area 4 between each other 43
There are four. As a result, the dynamic torque increases and the rolling surfaces 41 and 42 are easily worn.

In order to avoid this problem, in particular, in a ball screw used for swinging such as a grinding machine or an electric discharge machine, as shown in FIG. A spacer ball type in which every other small spacer ball 43a is arranged so as to be interposed therebetween is adopted, and the rotation direction between the adjacent balls 43, 43a is reversed to form a frictional force relaxation region 45. In addition to reducing the dynamic torque, the wear of the balls 43, 43a and the rolling surfaces 41, 42 of the ball screw grooves is reduced.

On the other hand, a ball screw used for an injection section, a mold clamping section, an eject section of an electric injection molding machine, an electric press machine, or the like is required to have a high load capacity. When the load disappears, the wear between the balls is reduced, so that a total load ball type has conventionally been adopted.

[0007]

FIG. 5 shows a typical cycle diagram of a ball screw used in a mold clamping portion, an injection portion, an electric press, and the like of an electric injection molding machine. The driving range is such that the stroke H is H ≦ 3 × L with respect to the lead L of the ball screw.
Often used in the range. The “load diagram” in the figure,
As shown in the “speed diagram”, the load applied to the ball screw increases from a no-load state to a stopped state by one drive, and the ball screw receives a maximum load when stopped. In an electric injection molding machine, this corresponds to a resin injection or a mold clamping process. Next, when the ball screw is driven in the opposite direction, the load decreases, and when the load completely disappears, the load on the internal balls becomes zero.Therefore, there is no competition between adjacent balls, and the dynamic torque increases. Should be gone.

However, the maximum load is applied when the ball screw is stopped, and in a motor deceleration region, the rotation speed of the ball screw is extremely low, close to zero. This makes it difficult for an oil film to be formed on the ball, which increases the friction between the balls and increases the dynamic torque.

The present invention can be applied to an application requiring a ball screw having a high load capacity, such as an electric injection molding machine or an electric press machine, without lowering the load capacity, and particularly by suppressing the wear of the ball in a low speed region. An object of the present invention is to provide a ball screw capable of preventing an increase in torque.

[0010]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a method in which a number of balls are rotatably accommodated between opposed ball screw grooves formed on a screw shaft and a nut, respectively. In the above ball screw, the balls are formed of a loaded ball for supporting a loaded load and a spacer ball having a smaller diameter than the loaded ball, and each of the balls is formed so that one spacer ball is interposed between the two loaded balls. And the swing stroke H of the screw shaft or the nut with respect to the lead L of the ball screw groove is H ≦ 3 × L
Is intended to be used in a limited manner.

The ratio between the number of the load balls and the number of the spacer balls is set to one of 1: 1, 2: 1, 3: 1 and 4: 1. It is possible to adopt a configuration in which the diameter difference is set so that a load is generated on the spacer ball at the time of the maximum load.

Further, it is also possible to adopt a configuration in which the use of the above-mentioned ball screw is limited to a swinging portion of a frequently used place under a high load load in an electric injection molding machine, an electric press machine or the like.

[0013]

Embodiments of the present invention will be described below with reference to the accompanying drawings. The embodiment shown in FIG. 1 relates to an electric injection molding machine, and particularly relates to an injection section 1 and a mold clamping section 2 thereof.

The injection section 1 is a section for moving an extrusion screw 4 inserted into the heating cylinder 3 in the axial direction thereof, and has a rotary drive source 5 composed of a speed reducer and a motor. The screw shaft 7 of the screw 6 is connected. The nut 8 fitted on the screw shaft 7 is integrated with the inner diameter surface of the cylindrical connecting member 9. One end of the connecting member 9 is connected to the rear end of the extrusion screw 4, and the extrusion screw 4 and the screw shaft 7 are concentrically arranged.

The extrusion screw 4 is rotatably and reciprocally supported by a bearing 10 inside the heating cylinder 3, and a serration 11 is formed at a rear end exposed to the outside of the heating cylinder 3. A gear 12 meshes with the serration 11 and is further connected to a rotation drive source 14 of the extrusion screw 4 via a gear 13 meshed with the gear 12. A hopper 15 for supplying a material is provided above the heating cylinder 3, and a heater 16 is mounted on the outer peripheral surface of the heating cylinder 3.

The resin material in the hopper 15 is sent forward by rotating the extrusion screw 4 by the rotary drive source 14, and is heated and melted by the heater 16.
When the rotation drive source 5 of the injection unit 1 is driven to rotate the screw shaft 7 of the ball screw 6, the nut 8 and the connecting member 9 integrated therewith are advanced, and the pushing screw 4 connected to the connecting member 9 is moved. Then, the molten resin in the heating cylinder 3 is injected into the fixed plate 18 from the nozzle 17 at the tip. When the injection of the resin is completed, the extruding screw 4 is rotated by the rotary drive source 14 in the direction in which the resin material is fed out, the resin material is sent out, and the extruding screw 4 is retracted by the rotation of the connecting member 9 and the nut 8, so that the next extrusion is performed. Prepare for.

On the other hand, the mold clamping portion 2 allows the fixing base 19 to rotatably support a nut 23 of the ball screw 22 via a bearing 21, and the nut 23 has a rotation drive source 24 comprising a motor and a reduction gear. Is transmitted to the nut 23 by the belt 25. Screw nut 2 on the nut 23
The movable plate 27 is connected to the tip of the screw shaft 26. The movable board 27 includes the fixed board 18 and the fixed base 19 described above.
Are slidably supported by a guide bar 28 provided therebetween, so as to approach and separate from the fixed plate 18. The mold 2 is provided on the opposite surface of the fixed plate 18 and the movable plate 27.
9, 29 'are mounted. Although not shown, the movable plate 27 is provided with a protruding pin for protruding a molded product so as to be able to protrude and retract.

The above-mentioned mold clamping unit 2 is provided with a rotary drive source 24.
By rotating the nut 23 by the rotation of the nut, the movable plate 27 is advanced in the direction of the fixed plate 18 together with the screw shaft 26, thereby clamping the molds 29 and 29 '. Further, the movable platen 27 is moved backward by reversing, and the molds 29, 2
Open 9 'to eject the molded product.

Since the ball screws 6 and 22 of the injection unit 1 and the mold clamping unit 2 have the same structure, the ball screw 6 is selected and described in detail below.

As shown in FIG. 2, a thread groove 31 is formed on the outer periphery of the screw shaft 7 of the ball screw 6, and a thread groove 31 'facing the above-mentioned thread groove 31 is formed on the inner peripheral surface of the nut 8. Is done.

Both ends of the thread groove 31 'of the nut 8 are connected by a circulation path (not shown). The above screw grooves 31, 3
A number of balls 32 are incorporated in 1 'and the circulation path.

As shown in FIG. 3 (a), the ball 32 is a load ball 32a which contacts the ball screw groove 31 of the screw shaft 7 and the ball screw groove 31 'of the nut 8 to support the load.
And a spacer ball 32b having a slightly smaller diameter and not in contact with both grooves 31, 31 'but in contact only with the load ball 32a. The ratio between the number of the load balls 32a and the number of the spacer balls 32b is shown in FIG.
In this case, the ratio is 1: 1, and both balls 32a and 32b are arranged alternately. In the case of FIG. 3B, the above ratio is 2: 1, and one spacer ball 32b is arranged for every two load balls 32a. Further, in the case of FIG. 3C, the ratio is 3: 1, and one for each of the three load balls 32a.
The spacer balls 32b are arranged.

Although not shown, a ratio of 4: 1 can be used.

3 (a) to 3 (c), the rotation directions of the balls 32a and 32b are indicated by arrows, and the friction alleviating area 34a and the friction increasing area 34b are shown. Balls 32a, 3
When the ratio of 2b is in the range of 1: 1 to 4: 1, there is an effect of reducing friction due to the interposition of the spacer balls 32b. However, when the ratio exceeds 2b, the friction increasing region 34b increases, so that the effect of reducing friction is reduced. Will be reduced.

A specific example is as follows. However, the diameter difference between the load ball 32a and the spacer ball 32b was selected such that a load was generated on the spacer ball 32b when the maximum load was applied.

The diameter d = φ63 of the screw shaft 7 and the lead L = 16
mm, ball diameter Dw = 1/2 inch, applied load F = 20
t, the ratio of the number of load balls to the number of spacer balls = 2: 1, and the difference in spacer ball diameter = 80 μm.

Although illustration is omitted, FIG.
As shown in (c), the ball screw of the spacer ball type in which the spacer ball 32b is mixed can be used for a press head driving device of an electric press.

In the ball screw of the above embodiment, the screw shaft swings when the nut is fixed, but the same applies to the case where the nut swings when the screw shaft is fixed.

[0029]

As described above, the ball screw of the present invention can prevent an increase in dynamic torque under load and increase the load of a drive motor in a high-load application such as an electric injection molding machine and an electric press machine. Can be suppressed. In addition, since friction between the balls is reduced, heat generation and wear of the balls are prevented,
The life of the ball screw can be extended.

[Brief description of the drawings]

FIG. 1 is a sectional view of an electric injection molding machine according to an embodiment.

FIG. 2 is a partial cross-sectional view of the ball screw according to the first embodiment;

FIGS. 3 (a) to 3 (c) are explanatory diagrams of various examples of the arrangement of balls in the above.

4 (a) and 4 (b) are explanatory views of a conventional ball arrangement.

FIG. 5 is a typical cycle diagram of a ball screw.

[Description of Signs] 1 Injection unit 2 Mold clamping unit 3 Heating cylinder 4 Screw 5 Rotation drive device 6 Ball screw 7 Screw shaft 8 Nut 9 Connecting member 10 Bearing 11 Serration 12 Gear 13 Gear 14 Rotary drive source 15 Hopper 16 Heater 17 Nozzle Reference Signs List 18 fixed board 19 fixed base 21 bearing 22 ball screw 23 nut 24 rotation drive source 25 belt 26 screw shaft 27 movable board 28 guide bar 29, 29 'mold 31, 31' screw groove 32 ball 32a load ball 32b spacer ball 34a friction Relaxation area 34b Friction increase area

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) B29C 45/66 B29C 45/66 (72) Inventor Kimito Ushida 1578 Higashikaizuka, Iwata City, Shizuoka Prefecture F term (reference) 4E090 AA01 AB01 BA02 BB04 CC04 CC10 HA07 4F202 CA11 CK41 CL39 4F206 JA07 JD03 JL02 JT38

Claims (4)

[Claims] 1. A ball screw comprising a plurality of balls rotatably accommodated between opposing ball screw grooves formed on a screw shaft and a nut, respectively. The above-mentioned ball is formed by a spacer ball having a diameter smaller than that of the load ball, and the balls are arranged so that one spacer ball is interposed between the two load balls. A ball screw characterized in that it is used only in applications where the swing stroke H of a shaft or a nut is H ≦ 3 × L. 2. The ball according to claim 1, wherein the ratio between the number of the load balls and the number of the spacer balls is set to one of 1: 1, 2: 1, 3: 1 and 4: 1. screw. 3. The ball screw according to claim 1, wherein a diameter difference between the load ball and the spacer ball is set such that a load is applied to the spacer ball at the time of a maximum load. 4. The method according to claim 1, wherein the application is limited to a swinging portion of a frequently used portion under a high load load in an electric injection molding machine, an electric press machine, or the like. Ball screw described in.